Market sizing
Checked against the source, not assumed.
Who to leave out is settled at the same moment as who to include. Standardisation happens before matching, never the other way round. Anything that could not be filled is stated plainly rather than padded.
Known-gap register
A written list of what the file does not contain, kept with the file.
Column reconciliation
Bringing differently named fields from separate feeds onto one agreed set of headings.
Change-only refresh
On a repeat build, reporting what actually moved instead of re-delivering the whole file.